In order to improve the convenience of electric automobiles that in recent years have begun to be widespread, it is very important that the distance traveled per one electric charge be lengthened by improving the efficiency of the electric motor. In order to improve the efficiency of the electric motor, using a compact electric motor that rotates at high speed, and transmitting the rotation of the output shaft of this electric motor to the driven wheels after reducing the rotating speed is effective. Of the reducers of an electric automobile, a first-stage reducer that is directly connected to the output shaft of the electric motor has a very fast operating speed, and it is necessary that vibration and noise be suppressed during operation. Therefore, use of a friction roller reducer as at least the first-stage roller is feasible. Friction roller reducers that can be used for this purpose are known and disclosed in JP 59-187154 A, JP 61-136053 A, and JP 2004-116670 A. Of these, conventional construction as disclosed in JP 2004-116670 A will be explained using FIG. 51 to FIG. 53.
This friction roller reducer 1 comprises an input shaft 2, and output shaft 3, a sun roller 4, ring-shaped roller 5, a plurality of planet rollers 6 as intermediate rollers, and a loading cam apparatus 7.
Of these, the sun roller 4 comprises a pair of sun roller elements 8a, 8b that are divided in the axial direction, and that are arranged concentrically around the input shaft 2 with a gap between the tip end surfaces of each and are capable of relative rotation with respect to the input shaft 2. The outer circumferential surfaces of these sun roller elements 8a, 8b are each provided with an inclined surface that is inclined in a direction such that the outer diameter becomes smaller going toward the tip end surface, and these inclined surfaces function as rolling contact surfaces. Therefore, the outer diameter of the rolling contact surface of the overall sun roller 4 is small in the middle section in the axial direction and becomes larger going toward both end sections.
Moreover, the ring-shaped roller 5 is overall ring shaped, and is supported by and fastened to a stationary portion such as a housing (not illustrated in the figure) so as to be arranged around the sun roller 4 and so as to be concentric with the sun roller 4. The inner circumferential surface of the ring-shaped roller 5 functions as a rolling contact surface and is inclined in a direction such that the inner diameter becomes larger going toward the center section in the axial direction.
The plurality of planet rollers 6 are arranged at a plurality of locations in the circumferential direction of a ring-shaped space 9 between the outer circumferential surface of the sun roller 4 and the inner circumferential surface of the ring-shaped roller 5. The planet rollers 6 are arranged so as to be parallel with the input shaft 2 and the output shaft 3, and each is supported around a planet shaft 10, which is a rotating shaft, by way of radial needle bearing so as to be able to rotate freely. The end sections of these planet shafts 10 and supported by and fastened to a carrier 11, which is a support frame, that is connected and fastened to the base end section of the output shaft 3. The outer circumferential surface of the planet rollers 6 is a convex curved surface having a generating line that is a partial arc shape, and each comes in rolling contact with the outer circumferential surface of the sun roller 4 and the inner circumferential surface of the ring-shaped roller 5.
Furthermore, the loading cam apparatus 7 is provided between one sun roller element 8a of the sun roller elements 8a, 8b and the input shaft 2. In order for this, a support ring 13 is fastened to the middle section of the input shaft 2 by a retaining ring 12, and a disc spring 14, cam plate 15 and a plurality of balls 16 as rolling bodies are located in that order from the side of the support ring 13 between the support ring 13 and the one sun roller element 8a. Driven-side cam surfaces 17 and driving-side cam surfaces 18 are provided at a plurality for locations in the circumferential direction of each the base end surface of the one sun roller element 8a and the surface on one side of the cam plate 15 that face each other. These cam surfaces 17, 18 are shaped such that the depth in the axial direction is the deepest in the center section in the circumferential direction, and gradually becomes shallower going toward both end sections.
As illustrated in FIG. 53A, this kind of loading cam 7 is such that when the input shaft 2 is stopped, the ball 16 is located in the deepest portion of the driven-side cam surface 17 and the driving-side cam surface 18. In this state, the elastic force of the disc spring 14 presses the one sun roller element 8a toward the other sun roller element 8b. On the other hand, as illustrated in FIG. 53B, as the input shaft 2 rotates, the ball 16 moves to the portion of the cam surfaces 17, 18 that are shallow. The space between the sun roller element 8a and cam plate 15 is opened up, and the sun roller element 8a is pressed toward the sun roller element 8b. As a result, the sun roller element 8a is rotated and driven while being pressed toward the sun roller element 8b with the larger force of the elastic force of the disc spring 14 and the thrust force that is generated by the ball 16 riding up on the cam surfaces 17, 18.
During operation of the friction roller reducer 1 described above, the space between the sun roller elements 8a, 8b is reduced by the thrust force in the axial direction that is generated by the loading cam apparatus 7. Also, the surface pressure at the rolling contact sections between the outer circumferential surface of the sun roller 4 that is constructed by these sun roller elements 8a, 8b and the outer circumferential surfaces of the planet rollers 6 increases. As the surface pressure increases, the planet rollers 6 are pressed outward in the radial direction of the sun roller 4 and ring-shaped roller 5. When this happens, the surface pressure at the rolling contact areas between the inner circumferential surface of the ring-shaped roller 5 and the outer circumferential surface of the planet gears 6 also increases. As a result, the surface pressure at a plurality of rolling contact areas between the input shaft 2 and output shaft 3, which are traction sections for transmitting power, increases according to the size of the torque to be transmitted between the input shaft 2 and the output shaft 3.
When the input shaft 2 is rotated in this state, this rotation is transmitted to the planet rollers 6 from the sun roller 4, and these planet rollers 6 revolve while rotating around the sun roller 4. The revolving motion of these planet rollers 6 is outputted by the output shaft 3 by way of the carrier 11. The surface pressure at the traction sections becomes proper according to the size of the torque that is to be transmitted between the input shaft 2 and the output shaft 3, so excessive sliding at the traction sections does not occur, and rolling resistance due to excessive surface pressure at traction sections does not uselessly increase.
During operation of the conventional friction roller reducer 1, the planet rollers 6 displace a small amount (for example a maximum of several hundred μm) in the radial direction of the sun roller 4 and ring-shaped roller 5 due to the movement of the loading cam apparatus 7. In other words, as the torque that is inputted to the friction roller reducer 1 from the input shaft 2 changes, the dimension in the axial direction of the loading cam apparatus 7 changes (expands or contracts), and the dimension on the radial direction of the portion of the one sun roller element 8a that has entered on the inside of the planet roller 6 changes. Due to this change, the planet rollers 6 displace in the radial direction of the sun roller 4 and the ring-shaped roller 5, however, in the construction illustrated in FIG. 51, this displacement is only allowed due to the elastic displacement of the planet shafts 10. Therefore, when the torque changes, displacement of the planet rollers 6 in the radial direction is not always performed smoothly, and it becomes easy for the surface pressure at the traction areas to become ununiform. When the surface pressure is not uniform, the transmission efficiency of the friction roller reducer 1 worsens.
As technology related to the present invention, construction that increases the operation response is disclosed in JP 2004-52729 A wherein in an apparatus in which the tip end section of a link is caused to engage with the groove in the radial direction of a drive ring and in a coil shaped groove of an intermediate rotating member, and the base end section of the link is connected to a lever of a driven shaft member, and a rotation operating force that is applied to the intermediate rotating member is converted to relative rotation between the drive ring and driven shaft member by way of the link, a weight adding section is provided in the link such that the centrifugal force due to the rotation of the apparatus does not act as a large moment on the link.